Influence of Raw Materials on the Carbothermal Synthesis of Single-Phase Aluminum Oxynitride Powder

Abstract:

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Aluminum oxynitride powders were synthesized by carbothermal reduction, using nano-sized
alpha-alumina, gamma-alumina and carbon as raw materials. Effects of the weight percentages of
alpha-alumina in alumina (R) and synthesizing temperatures (T) on the preparation of single-phase AlON
powders have been studied. The results showed that proper R can reduce the shrinkage and increase the
formation rate of AlON phase, but a high R will reduce the formation rate of AlON phase, because the
activity of alpha-alumina was lower than that of gamma-alumina. Single-phase AlON powder with
excellent properties can be obtained under the condition of R=0.15, T=1700°C. Moreover, this
single-phase AlON powder was well-dispersed with an average size of about 2 μm.

Abstract: Single-phase aluminum oxynitride powders were obtained by varying the holding temperature
(T) and the weight percentage of α-Al2O3 in Al2O3 (X) with nano-sized Al2O3 and AlN powders as raw
materials. Influences of T and X on the phase composition of obtained powders were studied. The results
showed that the content of aluminum oxynitride increased with increasing T or X. When X was 50% and
T was 1750°C, obtained powders had better properties than those of others.

Abstract: Transparent AlON ceramics are prepared with single-phase AlON powder synthesized from
micron-sized aluminum and nano-sized alumina. The ceramics are prepared through sintering at the
temperature of 1880°C for 10, 20 and 40 hours in flowing-nitrogen atmosphere, respectively. The effects
of powder and temperature holding-time on transparent ceramic preparation and microstructure and
transparency are investigated. The results show that all samples are transparent and of a single-phase
AlON and, with increasing holding-time, the average pore size and porosity decreases and consequently,
the ceramics are dense and their transparency is improved.

Abstract: Single-phase AlON powder was prepared by carbothermal reduction in flowing nitrogen
atmosphere, using nano-sized alumina and carbon powder as raw materials. Transparent AlON ceramic
samples using the single-phase powder were prepared by sintering at the temperature of 1880°C for 10h,
20h and 40h in flowing nitrogen atmosphere, respectively. It showed that the transparency and the density
of the ceramic samples increased with increasing temperature holding-time. And the microstructures of
the obtained samples were observed.

Abstract: The single-phase AlON powder used to prepare transparent ceramics was synthesized from
solid-state-reaction using nano-sized Al2O3 and AlN powders with high purity. An appropriate amount of
the powder was molded into pellets and isostatically pressed using polyvinyl alcohol as the binder. The
AlON ceramic samples were obtained by sintering the pellets at 1880°C for 10 h, 20 h and 40 h,
respectively. The transparency of the samples increased as the temperature holding time was prolonged.
The density, phase compositions and microstructures of the sintered samples were discussed in detail.

Abstract: In this paper, a carbothermal reduction and nitridation (CRN) synthesis for cubic aluminum oxynitride (γ-AlON) powders is reported. The CRN reaction was conducted via a two-step synthesis procedure at a heating rate of 100 °C/min. In the first step, the mixture of fine γ-Al2O3 and soluble starch was annealed at 1550~1580 °C for different duration. It is found that the mixture of α-Al2O3 and AlN with an appropriate ratio can be obtained by CRN reaction. The content of AlN in mixture is closely related with the reaction condition. In the second step, the as-received mixture of α-Al2O3 and AlN was heat-treated at 1700 °C for 10 min. The single phase γ-AlON powders with particle size less than 3 µm were obtained.